1. Field of the Invention
The present invention relates to a backlight module, and more particularly, to a backlight module with a light guide plate that is widened from the light entrance plane toward another side plane.
2. Description of the Prior Art
With the rapid development of technology, various kinds of intelligent information products are available to people living in modern societies. Flat display modules, such as liquid crystal display modules, have played quite an important role in information products. Since the flat display module has the characteristics of a light and portable configuration, low power consumption, no radiation pollution, and so on, it has been widely applied to portable information products, such as notebooks, personal digital assistants (PDAs), and cellular phones, etc.
Conventionally, a liquid crystal display device includes a backlight module for providing back light source to the liquid crystal display panel. Referring to FIG. 1, FIG. 1 is a sectional schematic view of a conventional backlight module 10. The conventional backlight module 10 contains a light source 12, a light guide plate 14, a reflector 22 disposed below the light guide plate 14, a housing 16, a plurality of optical films 18, and a printed circuit board (PCB) 20 disposed below the light source 12. The PCB 20 is used for transferring currents or control signals to the light source 12. The light exit plane 12a of the light source 12 faces the light entrance plane 14a of the light guide plate 14 and is positioned nearby the light entrance plane 14a. In addition, the position level of the light exit plane 12a of the light source 12 is approximately the same as the position level of the light entrance plane 14a of the light guide plate 14 so that light emitted from the light source 12 directly progresses into the light guide plate 14 through the light entrance plane 14a for avoiding light loss. The light guide plate 14 is a flat plate with a uniform thickness. As light progresses into the light guide plate 14, it will propagate in the light guide plate 14 and pass through the light exit plane 14b, the optical films 18 into the liquid crystal display panel (not shown).
As shown in FIG. 1, the PCB 20 has a certain thickness and has to be disposed below the light source 12, such that the part at the side of the light source 12 of the backlight module 10 is thicker than the thickness of the entire flat light guide plate 14. As a result, the housing 16 for containing all the elements of the backlight module 10 has to be designed with a deep containing space according to the total thickness of the part at the side of the light source 12 of the backlight module 10 for positioning the light source 12 and the PCB 20, while the other portion of the housing 16 for positioning the light guide plate 14 has a shallow containing space. Therefore, the housing 16 usually has a winding portion 24, which brings a difficulty in fabrication process of the housing 16. As mentioned above, the conventional backlight module 10 has a large thickness at the side of the light source 12, which is thicker than the side of the light guide plate 14. For example, the thickness difference between the two sides may be about 0.2 millimeters (mm) to 0.3 mm. However, it is an intolerable thickness difference for portable information products under a market requirement of light volume, and the thickness difference of two sides of the backlight module 10 also influences the whole design structures of the application electronic products. Accordingly, the design of structure of the conventional backlight module 10 has to be kept on study for meeting the market requirement of its application products.
Mostly, the conventional light guide plate 14 is formed by injection molding method, and the light guide plate 14 in the liquid crystal display device of common portable products is about 0.8 mm, which has reached the limitation of the injection molding technology. Furthermore, the yield of injection molding process decreases as the thickness of the light guide plate 14 reduces. Therefore, how to design the thickness or structure of the light guide plate 14 to conform to the current injection molding technology for producing the light guide plate 14 with a good yield is still an unsolved issue.